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| bio | website | lightandmatter.com |
|---|---|---|
| location | ||
| age | ||
| visits | member for | 1 year, 10 months |
| seen | 7 hours ago | |
| stats | profile views | 995 |
I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.
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11h |
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Why do prisms work (why is refraction frequency dependent)? @BrandonEnright: To me, the Lorentz model seems to imply that $n$ would be roughly temperature-independent, except for maybe a slight change in $N$ due to thermal expansion...? I think the papers I came across on the web seemed to indicate that the temperature dependence was quite small, and hard to measure. |
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14h |
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What is the wave length of the entire universe? Even if the universe is finite, it doesn't make sense to talk about its total momentum. There's a good discussion of this in Misner, Thorne, and Wheeler, p. 457. |
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21h |
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Difference between $\Delta$, $d$ and $\delta$ "We know that $\frac{dy}{dx}$ is always an operator and not a fraction, whereas $\frac{\delta y}{\delta x}$ is an infinitesimal change." The operator would be $d/dx$, not $dy/dx$. Also, it is actually valid to consider $dy/dx$ as the quotient of two infinitesimal numbers. That's how physicists, mathematicians, and engineers throught about it for hundreds of years after the invention of calculus, and Abraham Robinson proved ca. 1960 that it didn't lead to logical inconsistency. There is even a freshman calc book using this approach: math.wisc.edu/~keisler/calc.html |
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1d |
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Einstein Field Equations in other space-time dimensions than 3+1? @joshphysics: Maybe it's not really that important, but I think it might help to clarify the physics you're describing in the final paragraph, where you refer to black hole singularities in 3+1 dimensions. |
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1d |
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Why does sound move faster in solids? Density also matters, not just the restoring force. |
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1d |
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The Univere's mass-energy and uncertainty "The HUP is an inequality. It tells you that the mass must be at least this small number you give, it does not put bounds from above[...]" No, the OP has the inequality the right way around. In the traditional hand-wavy application of the energy-time uncertainty relation to the creation of pairs of virtual particles, the logic is that the energy of the pair has to be less than a certain amount, because if it were more than that, the violation of conservation of energy would be detectable despite the HUP. |
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1d |
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The Univere's mass-energy and uncertainty Duplicate of physics.stackexchange.com/q/2838/4552 |
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1d |
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The Univere's mass-energy and uncertainty The web page in the first link discusses the mass of the observable universe, which isn't what's relevant here. |
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1d |
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How the value of permitivity of free space is determined? related: physics.stackexchange.com/q/3644/4552 physics.stackexchange.com/q/64841/4552 |
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1d |
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How can the big bang occur mathematically? Why the downvote? |
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1d |
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Why does sound move faster in solids? Viscosity and dissipation don't related to the speed. |
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1d |
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How the value of permitivity of free space is determined? These days it has a defined value. WP describes the history. en.wikipedia.org/wiki/Permittivity_of_free_space#Value |
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2d |
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What happens when non-equal voltages are put in parallel? The junction rule isn't going to be relevant, because there are no junctions (except in the trivial sense that constancy of current around a single-loop circuit can be considered to be an application of the junction rule). |
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2d |
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What happens when non-equal voltages are put in parallel? Voltage doesn't flow. Current flows. This is essentially just a short circuit. If you're talking about batteries that are assumed to be idealized voltage sources, then this is one of those questions like, "Can God make a rock so heavy that He can't move it?" A simpler question that raises the same issues is what happens when you short across an ideal voltage source with a perfectly conducting wire. If these are non-idealized batteries, you could probably get a variety of effects depending on the batteries' internal resistances, their electrochemistry, and other factors. |
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2d |
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How can the big bang occur mathematically? "If causality is absolutely correct then there would need to be something before the big bang to make it happen." Not true. In classical GR, we have a universe at all times $t>0$. For every time $t$, there is another time $0<t'<t$ that could be considered to have caused $t$. The way GR captures causality is with the notion of a globally hyperbolic spacetime (Hawking and Ellis, p. 206). Realistic cosmological models using GR are globally hyperbolic. |
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2d |
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Einstein Field Equations in other space-time dimensions than 3+1? You can have conical singularities in 2+1 dimensions. |
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2d |
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What determines the angle of the cushion on a pool table? @Pulsar: Ha! What an ignominious solution to an elegant physics problem! If you turn your comment into an answer, I'll accept it. |
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May 22 |
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Is it possible to reproduce Double-slit experiment by myself at home? duplicate or near-duplicate of physics.stackexchange.com/questions/38440/… |
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May 21 |
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Is electromagnetism a dead research field? Are you talking about purely classical electromagnetism, or does your question include quantum effects? Do you want to include general relativity, or only special relativity? |
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May 21 |
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How does moving charges produce magnetic field? related: physics.stackexchange.com/questions/3618/… |
